Stored energy combustors have long been utilized for producing hot gases under pressure to operate turbine engines. In such stored energy combustors, a carbonaceous fuel is typically combusted with an oxidant to produce hot gases of combustion, and additional fuel may typically be introduced into the hot gases of combustion to be vaporized, or partly decomposed, or both. By so doing, the volume of hot gas can be increased while bringing the temperature of the combustion gas down to a temperature incapable of causing damage to the turbine engine.
One difficulty in the operation and use of such stored combustors is carbon buildup which results when the fuel is not completely oxidized and elemental carbon is formed within or downstream of the combustion chamber. It is important to keep the internal walls of the stored energy combustor free of carbon buildup since such carbon can break away and cause damage to downstream components and can also impair the efficiency of the combustor and turbine engine. To this end, carbon buildup can be avoided by providing an excess of oxidant within the combustion chamber but this necessarily results in excessive consumption of oxidant during operation of the stored energy combustor.
On the other hand, there is ordinarily a plentiful supply of liquid fuel in most cases. It has thus been conventional practice to run stored energy combustors on the rich side so that all available oxidant is consumed during combustion to thereby minimize oxidant consumption. However, by so doing, the potential for carbon buildup is increased.
As pointed out in Parrin U.S. Pat. No. 1,828,784, issued Oct. 27, 1931, it is also desirable to cool the combustion chamber to prevent damage thereto by excessive heat from combustion occurring therein. Advantageously, this is accomplished by cooling the combustion chamber with fuel, but the fuel may get overly hot causing gumming up leading to rapid failure and, furthermore, the fuel starts to boil which makes fuel injector design difficult and causes serious control system instabilities. At lower power settings, this fuel overheating is particularly troublesome because the low pressure in the combustion chamber results in fuel boiling at even lower temperatures.
As already suggested, carbon buildup is undesirable because it may interfere with heat transfer, but another problem resulting from carbon buildup is much more serious. Specifically, stored energy combustors are frequently used to produce hot gases for driving a turbine wheel. As carbon builds up, particles thereof typically break free and then flow with the hot gases of combustion through the turbine wheel. Unfortunately, particulate carbon is known to erode the turbine nozzle and the turbine wheel. Furthermore, carbon deposits can build up on the surface of the turbine nozzle and restrict the flow of hot gases to the turbine wheel which can cause an undesired performance loss.
Still another problem associated with excessive carbon production is the existence of a massive black exhaust plume which is highly undesirable.
Presently, it is believed that a substantial portion of the carbon produced is a result of liquid phase pyrolysis during liquid fuel droplet evaporation. It is also quite likely that some gas phase carbon is produced as the result of the cracking reactions which occur in practice. However, the gas phase carbon is on the molecular level and much less harmful than liquid phase carbon which is on the order of microns for purposes of comparison.
Since it is believed that the carbon is a result of liquid phase pyrolysis, it is essential to achieve rapid fuel evaporation. This is the best known manner of minimizing liquid phase carbon. However, stored energy combustors have not been entirely satisfactory in addressing these serious carbon problems.
While addressing all of the foregoing problems, it is also necessary to make it possible to achieve ignition without any substantial difficulty which can be accomplished by enlarging the combustor to reduce velocity. However, this is known to produce a problem in terms of oversizing. Accordingly, any practical solution must take into account weight and spacing savings in the combustor, reduction in propellant consumption by enhanced cracking, and consequent substantial reductions in carbon and smoke.
The present invention is directed to overcoming one or more of the foregoing problems and achieving one or more of the resulting objects.